Today's portable rechargeable devices are typically recharged by temporarily connecting them to a recharger via a mating plug-in or clip-on connection. An example is the typical “floating wire” connection between a mains charger and a mobile phone (see FIG. 1).
The connection serves two purposes:                1) It electrically connects the device to its recharger, allowing transfer of power.        2) It mechanically connects the device to its recharger, in a way which retains it securely against forces from accidental knocks and the like, but is easily removable by the user. This mechanical connection thus allows recharging to continue reliably until the user physically breaks the connection, and in some cases may also keep the device conveniently available to the user. Examples of the latter include the recharging “cradle” for the Palm Pilot® and the drop-in “hands-free” car socket for a mobile phone.        
Some of today's portable rechargeable devices are charged by a non-contact means, for example by inductive power transfer. An example is the Braun® electric toothbrush, where the toothbrush must be accurately located onto a spigot on the recharger, which retains it. However, the spigot serves only as a positioning means and no additional force is required to separate the toothbrush from the charger other than that required to lift the toothbrush against gravity.
But some of these non-contact charging means do not require the device and the recharger to be so precisely aligned. Such solutions may offer significant freedoms for the designer and for the user. For example the recharging means may be a laminar surface upon which a device can conveniently be placed, in any position and any orientation, as disclosed, for example, in the present applicant's UK patent application no. 01283175 of 27 Nov. 2001. This avoids the limitations of the positive mechanical connection (e.g. cradles, connectors, clips) required by other charging solutions, and so is more convenient to the user because it is easier to place a device casually anywhere on a surface than precisely to align it with a mechanical socket. Dispensing with the need for mechanical location may also allow other benefits, such as the ability simultaneously to recharge multiple units, and/or to recharge devices of different types on the same recharger.
However in some situations, the lack of positive mechanical retention of such a surface may be a disadvantage for users. For example:                A flat recharging surface must be kept substantially horizontal to prevent devices from sliding off the surface. But this requirement may be inconvenient to the user—for example putting the surface on a desk may occupy otherwise-useful space. Freeing-up the surface so that it can be placed in any orientation would give the user much more flexibility to use otherwise-useless space—for example to mount the surface vertically on a wall, or even on the inside of a car roof.        If a mobile recharging surface is likely to be subject to movement (e.g. a tabletop that may get knocked, or in a car, airplane or spacecraft), the devices may fall off.        
Clearly, it would be convenient to remove these potential disadvantages whilst preserving the benefits of freedom of design and use of such surface-based charging systems.